replace ioutil with io and os (#2327)

set the go version to 1.16 in pr.yml and tests.yml, so as to be consistent with the version in go.mod.

plugins/registry/kubernetes/client/api/response.go

@@ -3,7 +3,7 @@ package api
 import (
 	"encoding/json"
 	"errors"
-	"io/ioutil"
+	"io"
 	"net/http"
 
 	log "go-micro.dev/v4/logger"
@@ -84,7 +84,7 @@ func newResponse(res *http.Response, err error) *Response {
 
 	log.Errorf("K8s: request failed with code %v", r.res.StatusCode)
 
-	b, err := ioutil.ReadAll(r.res.Body)
+	b, err := io.ReadAll(r.res.Body)
 	if err == nil {
 		log.Error("K8s: request failed with body:")
 		log.Error(string(b))

plugins/registry/kubernetes/client/client.go

@@ -3,7 +3,6 @@ package client
 import (
 	"crypto/tls"
 	"errors"
-	"io/ioutil"
 	"net/http"
 	"os"
 	"path"
@@ -54,7 +53,7 @@ func detectNamespace() (string, error) {
 	}
 
 	// Read the file, and cast to a string
-	if ns, e := ioutil.ReadFile(nsPath); e != nil {
+	if ns, e := os.ReadFile(nsPath); e != nil {
 		return string(ns), e
 	} else {
 		return string(ns), nil
@@ -97,7 +96,7 @@ func NewClientInCluster() Kubernetes {
 		log.Fatal(errors.New("no k8s service account found"))
 	}
 
-	token, err := ioutil.ReadFile(path.Join(serviceAccountPath, "token"))
+	token, err := os.ReadFile(path.Join(serviceAccountPath, "token"))
 	if err != nil {
 		log.Fatal(err)
 	}

plugins/registry/kubernetes/client/utils.go

@@ -5,7 +5,7 @@ import (
 	"encoding/pem"
 	"errors"
 	"fmt"
-	"io/ioutil"
+	"os"
 )
 
 // COPIED FROM
@@ -31,7 +31,7 @@ func certificatesFromFile(file string) ([]*x509.Certificate, error) {
 	if len(file) == 0 {
 		return nil, errors.New("error reading certificates from an empty filename")
 	}
-	pemBlock, err := ioutil.ReadFile(file)
+	pemBlock, err := os.ReadFile(file)
 	if err != nil {
 		return nil, err
 	}